Method for forming a gravel pack in a well bore



L. A. LAYNE June 25, 1940.

METHOD FOR FORMING A GRAVEL PACK IN A WELL BORE Filed Dec. 23, 1938 2554/5 A. LAY/V5 INVENTOR.

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Patented June 25, 1940 METHOD FOR FORMING A GRAVEL PACK IN A WELL BORE Leslie A. Layne, Houston, Tex., assignor to The Texas Company, a corporation of Delaware Application December 23, 1938, Serial No. 247,400

Claims. (01. 16621) The invention relates to a method of depositing gravel in a cavity in a well bore in order to form a gravel pack or filter through which the fluid from the formation will be required to pass 5 as it fiows to the surface.

It is very important that the gravel bed or filter pack be properly deposited in a condition so that the granular particles will be free of contaminating matter such as the drilling mud which is usually in the well bore at the time the gravel is deposited andso that it is also free of sand and other particles which become mixed with the gravel as it is developed.

It is therefore one of the objects of the invention to wash and agitate a granular material as it is being deposited by passing through it from below a stream of liquid which will remove the carrier liquid and drilling mud as well as other foreign material from the granular particles.

Another object of the invention is to simultaneously deposit a stream of gravel and to subject the gravel as it is being deposited to a washing or agitating action of a stream of liquid from below.

Another objector the invention is to discharge from a string of pipe in a well bore a stream of liquid which will intermingle with gravel particles being deposited to cleanse the particles and settle them into desired filtering position.

It is also an object to so proportion the relative sizes of the strainer pipe and the wash pipe so that the resistance to flow between a unit of length of the pipes will be greater than the resistance to flowing of the liquid thru the gravel pack outside the strainer so that liquid discharging from the wash pipe will tend to flow upwardly thru the gravel rather than between the pipes.

. Still another object of the invention is to agitate the particles of gravel as they are being deposited in the well bore so as to erode the face of the formation and in this manner enlarge the well bore and to simultaneously carry away the eroded material so as to leave the gravel pack clean and in condition to serve as a filter bed.

Still another object of the invention is 'to agitate a gravel pack being formed by opposing the flow of carrier liquid with a stream of clear liquid so that each particle of gravel is washed as it is deposited.

Still anotherobjcct of the invention is to oppose the depositing ol" granular particles by floating them into position with a stream of liquid which opposes the settling of the gravel particles.

Still another object of the invention is to proi vide opposing flows of liquid in a well cavity where granular material is being deposited so that a stagnant area will be formed where the opposing flows meet in such a manner that the granular material carried by the downwardly moving stream will be transferred to the upwardly mov- 5 ing stream which will wash the granular particles and permit them. to settle in a clean and compact deposit.

It is also an object of the invention to erode the face of a producing formation by agitation of 10 the granular material and to simultaneously carry away the eroded material so that the gravel pack is clean as it is finally deposited so that a seal may be formed to entrap the gravel in its final position.

Other and further objects of the invention will be readily apparent when the following description is considered in connection with the accompanying drawing, wherein:

Fig. 1 is a side elevation of the upper end of 20 a well bore which is beinggravel packed by the present method and equipment.

Fig. 2 is a continuation of the side elevation of Fig. 1 and illustrating the lower end of the well bore wherein the cavity is being filled with gran- 25 ular material.

A well bore 2 has been drilled through the earth formattion down to the elevation of a productive formation 3 which is preferably oil or gas producing formation. It is desirable of course to 30 provide as large a cavity to receivethe granular pack or filter as possible so that the rate of flow at the face of the porous formation-will be as low as possible and of course the larger the diameter of the cavity provided the lower will be the rate 35 of flow because the unit area production will be less. With this in mind the well bore 2 has been underreamed 01' enlarged by mechanical means such as an underrcamer to provide the cavity 4 as seen in Fig. 2. There are certain limits to me- 40 chanical underreamers ofthis sort but as seen in the lowermost portion of Fig. 2 the well bore has been finally enlargedto provide the exposed face 5.

As is usual a casing 1 has been disposed in the 45 upper reaches of the well bore 2 and this casing has been cemented at 8 to anchor it firmly in position in order to support the well head equipment indicated generally at 9.

In order to introduce the gravel or granular 50 material In into the well bore a flow line connection H is made at the top of the casing l. The casing is then closed by a casing head l2 which carries the packing I3 to provide a seal around the production string l4. A production head I5 carries a flow line I 6 which is controlled by a valve II. A stufllng box l3 forms a seal about a wash line 20 which extends downwardly into the well inside of the production string H.

The production string 14 carries a packer 22 and a strainer section 23 which has the set shoe 24 connected on the lower end thereof. All of these parts are assembled as shown in Figs. 1 and 2prior to the introduction of any of the gravel II.

The gravel III is introduced into the flow line II from a suitable source of liquid under pressure which serves as a carrier liquid to move the granular material through the flow line 2| and in this manner force it into the annular space 25 between the casing and the production string. The gravel moves downwardly by gravity as well as due to the circulation of the carrier liquid and will discharge from the lower end 26 of the casing as seen in Fig. 2. The cavity 4 will probably be filled with a heavy drilling mud which has been used during the drilling and underreaming operations by which the cavity 4 was formed. This granular material will naturally move out to substantially the form indicated in Fig. 2 as it is released into the cavity 4.

Simultaneously with the introduction of the carrier liquid and gravel through the casing I there will be effected a discharge of circulating or agitating liquid through the wash pipe 20. This liquid is introduced from a suitable source such as a pump and is forced downwardly through the washline where it discharges into the shoe 24. An opening 21 at the base ofthe shoe may be used to discharge this liquid if the shoe is raised slightly off bottom. If it is desired to place the shoe on bottom then the discharge of this liquid will be from the apertures 28 which may be outwardly and upwardly inclined as shown. In either event this liquid will discharge into the bottom of the cavity 4 and will naturally move outwardly radially in the cavity and will tend to dilute and gradually displace the heavy drilling mud which is in the cavity 4.

In view of the fact that the carrier liquid coming down through the annular space 25 is moving downwardly and carrying the gravel and the fact that the circulating liquid discharging from the shoe 24 tends to wash the bottom of the well, it seemsobvious that where these two streams of liquid come into contact and engagement with each other that there will be a relatively stagnant area where liquid isneither moving upwardly nor downwardly. This contact of the two flowing streams will tend to distribute both streams and cause them to flair out and impinge against the periphery of the cavity 4. The gravel brought into the cavity by the carrier liquid :will be carried along with the two liquids as they are mixed together and thrown sharply against the face of the formation 3. Formations of this sort are usually of fine sand and this action of the gravel will tend to erode the formation so as to enlarge the cavity as indicated at 5.

The gravel will of course gradually settle through the circulating liquid and it is intended that the gravel will be gradually deposited as seen in Fig. 2. There will be a gradual erosion of the walls of the well so that the shoulder 30 being formed by the gravel close to the top of the deposit thereof will gradually move upwardly as the gravel accumulates. The gravel, being of greater specific gravity than the circulating liquid, will gradually settle through the liquid while the circulation of the liquid tends to carry along with it any fine particles of sand and other extraneous matter. At the same time the surface of each particle of gravel is washed free of mud and its contact with the other particles of gravel and with the wall of the cavity tends to clean the particles of gravel so that as the gravel rises in its final position the entire gravel pack will be relatively clean and there will be little or no extraneous matter mixed with the gravel.

One of the particular features of this manner of agitating the gravel as it moves out of the carrier liquid against the walls of the formation and into the circulating liquid is that the circulating liquid is forced upwardly through the gravel so that the deposit of the gravel to its final position is delayed and only the heavier particles will settle through the upwardly flowing stream of circulating liquid.

In actual tests it has been found that very little excessive pressure is required to force the cir-. culating liquid upwardly through the gravel because of the fact that the gravel is agitated and rinsed by the flow of such liquid; whereas, if an attempt is made to force the carrier liquid downwardly through the gravel, there is a tendency to pack the gravel and an excessive pressure is needed to eifect such a circulation. Furthermore, such a downward circulation is detrimental because it forces the mud and carrier liquid downwardly through the gravel which has already been deposited.

It. will be understood that the liquid, after it has deposited the gravel, will enter the strainer or screen 23 and flow upwardly to the surface through the area 32 between the production string and the wash line.

By proportioning the volume and rate of discharge of the circulating liquid as compared to the carrier liquid, it would seem clear that any desired amount of agitation can be accomplished, and secondly, any desired amount of erosion of the producing formation.

Fig. 2 shows a'seat plate 23 in the shoe 24 to receive the wash pipe 20 and to prevent the return of'circulating liquid upwardly inside of the strainer 23. This plate may be dispensed with however and the relative sizes of the strainer pipe 23 and the wash pipe 20 so proportioned that the annularspace 3| between them will cause a resistance to flow of the circulating liquid to such an extent that the circulating liquid will discharge from the strainer and flow upwardly thru the granular material in the cavity. Thus the resistance per unit of length between the pipes will be greater than the resistance per unit of length thru the gravel so that the flow will be out against the walls of the cavity.

Broadly the invention contemplates that a gravel pack or filter bed will be formed by gradually flowing the granular material into its final position while washing it free of extraneous matter.

What is claimed new is:

1. A method of depositing granular material about a strainer in a well cavity including the steps of inserting a production string of pipe and a strainer in the well bore, providing a wash line of pipe inside of said strainer and production pipe, introducing granular material and a carrier the wash pipe liquid upwardly thru the gravel than upwardly inside of the strainer around the wash pipe so that both the carrier liquid and the wash pipe liquid will enter the strainer adjacent the top thereof so that the stagnant area of liqdid in the cavity will be adjacent the top of the granular deposit and the deposited gravel will be agitated and washed by the upward flow of wash pipe liquid.

2. A method of depositing granular material about a strainer in a well cavity including the steps of inserting a production string of pipe and a strainer in'the Well bore, providing a wash line of pipe inside of said strainer and production pipe, introducing granular material and a carrier liquid into the bore about the production string of pipe, introducing a flow of liquid into the wash line to discharge from the bottom of the strainer, so proportioning the size of the wash pipe relative to the inside diameter of the strainer such that there will be a lesser resistance to flow of the wash pipe liquid upwardly thru the gravel than upwardly inside of the strainer around the wash pipe so that both the carrier liquid and the wash pipe liquid will enter the strainer adjacent the top thereof so that the stagnant area of liquid in the cavity will be adjacent the top of the granular deposit and the deposited gravel will be agitated and washed by the upward flow of wash pipe liquid, and thereafter setting a packer to seal the production string in the wall to confine the gravel.

3. A. method of depositing granular material about a strainer in a well cavity including the steps of inserting a production string of pipe and a strainer in the well bore, providing a wash line of pipe inside of said strainer and production pipe, introducing granular material and a carrier liquid into'the bore about the production string of pipe, introducing a flow of liquid into the wash line to discharge from the bottom of the strainer, so proportioning the size of the wash pipe relative to the inside diameter of the strainer such that there will be a lesser resistance to flow of the wash pipe liquid upwardly thru the gravel than upwardly inside of the strainer around the wash pipe so that both the carrier liquid and the wash pipe liquid will enter the strainer adjacent the top thereof so that the stagnant area of liquid in the cavity will be adjacent the top of the granular deposit and the deposited gravel will be agitated and washed by the upward flow of wash pipe liquid, and selectively varying the rate of introduction of gravel and carrier liquid and the wash pipe liquid so as to wash the deposited gravel and remove extraneous matter.

4. A method of depositing, washing and settling a body of granular material in forming a gravel pack in a well bore which includes the steps oi. introducing two streams of liquid simultaneously into the well, one of said streams being introduced into the top of the well to flow downwardly through the bore to the bottom of the well, the other stream being conducted separately from said first stream and discharged into the bottom of the well to flow upwardly to meet the down moving stream so as to provide a stagnant area or zone at the interface between said streams, and introducing the granular material into the stream entering the top of the well so that the granular material will settle out in said stagnant zone and be washed and deposited in the well bore.

5. A method of simultaneously depositing and washing a body of granular material in forming a gravel pack in well bores which includes the steps of introducing the granular material and a carrier liquid therefore at the top of the well so that the granular material will flow downwardly in the well bore, and simultaneously introducing a circulating or washing liquid into the well to discharge at the base of the well to flow outwardly to carry granular material against the side walls of the well bore to erode the formation and enlarge the wellbore, while carrying sand and foreign matter from the granular material as it set tles through the circulating liquid.

' LESLIE A. LAYNE. 

